Control arrangement for air ventilating and air heating systems having automatic reset and manual reset safety devices

ABSTRACT

AN IMPROVED CONTROL SYSTEM FOR AN AIR HEATING AND AIR VENTILATING APPARATUS HAVING A MULTI-VOLT ELECTRICAL POWER SOURCE , A FIRST POWER CONTROL CIRCUIT FOR ENERGIZING AIR VENTILATING MEANS, AND A SECOND POWER CONTROL CIRCUIT FOR ENERGIZING THE AIR VENTILATING MEANS AND AN AIR HEATING MEANS, THE SECOND POWER CIRCUIT INCLUDING SAFETY CONTROL MEANS FOR ENERGIZING THE SECOND POWER CONTROL CIRCUIT IN RESPONSE TO AN UNSAFE OPERATING CONDITION AND MEANS TO ENERGIZE FUEL PREHEAT MEANS AT RELATIVELY LOW TEMPERATURES.

United States Patent [1 1 Kirk [ CONTROL ARRANGEMENT FOR AIR VENTILATINGAND AIR HEATING SYSTEMS HAVING AUTOMATIC RESET AND MANUAL RESET SAFETYDEVICES [75] Inventor: Harold L. Kirk, Kirkwood, Mo.

[73] Assignee: American Air Filter Company, Inc.,

Louisville, Ky.

[22] Filed: Oct. 3, 1972 [2 11 Appl. N0.: 294,557

[52] US. Cl. 431/37, 236/9 [51] Int. Cl. F23n 5/20 [58] Field ofSearch..... 237/8 R; 236/11, 9; 431/36,

[561 References Cited UNITED STATES PATENTS 3,092,095 6/1963 Hottenrothet al. 431/37 X 1 Feb. 26, 1974 2,862,666 l2/l958 Kriechbaum 236/ll XPrimary ExaminerWilliam E. Wayner [57] ABSTRACT An improved controlsystem for an air heating and air ventilating apparatus having amulti-volt electrical power source, a first power control circuit forenergizing air ventilating means, and a second power control circuit forenergizing the air ventilating means and an air heating means, thesecond power circuit including safety control means for energizing thesecond power control circuit in response to an unsafe operatingcondition and means to energize fuel preheat means at relatively lowtemperatures.

6 Claims, 2 Drawing Figures PATENTEDFEB261974 3.794.460

' sum 1 0F 2 PATENTEDFEBZSIQH SHEET 2 0F 2 CONTROL ARRANGEMENT FOR AIRVENTILATING AND AIR HEATING SYSTEMS HAVING AUTOMATIC RESET AND MANUALRESET SAFETY DEVICES BACKGROUND OF THE INVENTION In recent years therehas been a considerable amount of research and development in the areaof control arrangements for air heating and air ventilating apparatus.Many different control arrangements are taught in the prior art whichinclude multi-volt electrical power sources and power control circuitsfor energizing air ventilating and air heating means either separatelyor in combination. Many of these control arrangements include safetycontrol devices to de-energize the power control circuits in response tounsafe operating conditions.

SUMMARY OF THE INVENTION In the present invention, it is recognized thatit is desirable to provide a control arrangement for an air heatingapparatus including air ventilating means for use in temperaturesranging from about 65F. to about 125F. Furthermore, it is recognizedthat it is desirable to include automatic reset and manual reset safetydevices to control air heating apparatus at ambient temperatures of fromabout 65F. to about 125F.

The present invention advantageously provides a straight-forward controlarrangement for an air heating and air ventilating apparatus including amulti-volt electrical power source, two power control circuits, onebeing to operate an air heating and ventilating apparatus and the otherbeing to operate an air ventilating apparatus separately from the airheating apparatus, the power control circuits including safety controldevices for controlling and resetting the air heating apparatus inrelation to unsafe conditions. The present invention further providesfor thermostat means operable at a preselected low temperature toenergize control preheat means prior to energization of an air heatingapparatus.

Various other features of the present invention will become obvious tothose skilled in the art upon reading the disclosure set forthhereinafter.

More particularly, the present invention provides a control arrangementfor an air heater having air blower means and air heating meansincluding automatic and manual resetting safety devices, the controlarrangement comprising: (a) a multi-volt electrical power source; (b) afirst power control circuit connected to the source and operable whenenergized to cause energization of air blower means, the first powercontrol circuit including relay switch means operable in one position tomaintain energization of the first power control circuit under normaloperating conditions and operable in an opposite position to de-energizethe first power control circuit; and, (c) a second power control circuitconnected to the source and operable when energized to causeenergization of the air blower means and an air heating means, thesecond power control circuit including relay switch means operable inone position to energize the air heating means and in an oppositeposition to de-energize the air heating means, the second power controlcircuit including thermostat means operable at a preselected lowtemperature in one position to energize fuel preheat means, the fuelpreheat means being energized for a preselected period of time prior tothe relay switch means being operable to energize the air heating means.

In accordance with a preferred embodiment of the invention, the controlarrangement includes one circuit called a first power control circuitand another circuit which will be called a second power control circuit.The first power control circuit controls the operation of relays andother means through which electrical power is delivered to theventilating fan. The second power control circuit controls the operationof relays and other means through which electrical power is delivered tothe air heating means as well as the ventilating fan. The second powercontrol circuit includes a number of normally closed switches operableto an open position in response to unsafe operating conditions and alsoincludes a thermostat means to energize the liquid fuel preheaters atrelatively low ambient temperatures of, for example, below 25F,- thepreheaters being energized for a selected period of time before thecombustion air blower, ventilating air blower and the fuel pump motorare energized.

Preferably, a time delay arrangement is provided in the second powercircuit in order to allow the fuel preheaters an opportunity to preheatthe liquid fuel before the combustion air blower, ventilating air blowerand the fuel pump motor are energized. It is further preferable thatboth the combustion air motor and the fuel pump motor are connected inparallel so that they may be energized at the same time in response to atime delay arrangement, the time delay actuating the combustion airmotor and the fuel pump motor after a preselected period of timesufficient to allow the preheaters to preheat the liquid fuel.

The invention will be described in connection with the accompanieddrawing, illustrating the embodiment 4 thereof by way of the example,and wherein:

FIG. 1 is a largely diagrammatic representation of one kind of airheating apparatus to which the invention may be applied; and,

FIG. 2 is a schematic representation of a controlled arrangementembodying the invention.

It is believed that the invention will be more readily understood if itis explained as applied to one type of air heater adapted for use withthe controlled circuit arrangement of the present invention. Thus, theFIG. 1 representation of an air heater is provided for showing certainbasic elements included in such a heater.

In FIG. 1, a first heat exchanger 102 containing a fuel gas burner 104,fuel gas burner 104 being provided to heat liquid which is pumpedthrough a continuous circuit including the liquid pump 106, liquid line108, second heat exchanger or coil 1 10 and liquid line 112 back to thefirst heat exchanger 102. The air is forced through the coil by anelectrically powered blower assembly 114 and the heating air isconducted from the outlet ll6 on the opposite side of the heat exchangerthrough ducts (not shown) to be served.

The power control circuits for controlling operation of certain parts ofthe FIG. 1 apparatus are shown in FIG. 2. All of the circuitry requiredfor operating the apparatus of the nature as illustrated in FIG. 1 isnot included in FIG. 2, FIG. 2 illustrating those parts of the circuitryhereinafter characterized as the first power control circuit and thesecond power control circuit. The first power control circuit is socharacterized because it controls the operation of the switches throughwhich the air ventilating fan 114 is operable and the second powercontrol circuit is so characterized because it controls the operation ofthe switches through which the power for the fuel gas heating apparatus104 and the air ventilating fan 114 of FIG. 1 is delivered.

Under normal starting conditions, if air ventilation is all that isrequired, the first power control circuit is actuated to causeenergization of the air ventilating fan 114. If air heating is required,the second power control circuit is actuated and serves to causeenergization in sequence the fuel preheat means 61, the ventilating fan114, and then simultaneously the combustion air blower 24 and the fuelpump motor 26 which supplies combustion air and fuel to the fuel gasburning apparatus 104. The manner in which this is accomplished by thecircuit of FIG. 2 will now be described.

Lines 100 and 101 are connected to a multi-volt power source, (notshown). With the start switch 20 closed, the ventilating fan contactor 1will be energized through normally closed contact 11 of safety relay l6and normally closed contact 9 of time delay relay 6. Energization ofcontactor 1 closes normally open contacts 3 and 5 thereby energizing theair ventilating fan motor 4. The time delay relay 6 includes theaforementioned normally closed contact 9, a ventilating fan pressureswitch 8 and a timing element 7, the ventilating fan pressure switch 8being operable to an open position as soon as the ventilating fan 114reaches a predetermined pressure and timing element 7 being in serieswith switch 8 to operate normally closed contact 9 to an open positionin a relatively short period of time, for example, 5 seconds. Thus, atthe end of 5 seconds if the air ventilating fan 114 has not obtained asufficient pressure to open pressure switch 8 thereby deactivatingtiming element 7, timing element 7 will open contact 9 which willde-energize ventilating fan contactor 1 opening the circuit includingthe air ventilating fan motor 4. A warning means, such as red warninglight 21, is included in the circuit parallel to the timing element 7and in series with the normally closed contact 8 wherein the warninglight 21 will be venergized as long as pressure switch 8 is in itsnormally closed position. Thus, if within 5 seconds the air ventilatingfan 114 does not reach the predetermined pressure which causes switch 8to open thereby deenergizing warning light 21, light 21 will remain onadvising the operator of a malfunction of the air ventilat-,

ing fan 114. Time delay relay 6 is generally adapted to reset itselfautomatically, therefore the aforementioned sequence of energization ofthe elements of the first power control is repeated, if necessary, untilthe ventilating fan pressure switch 8 is actuated by the air blower ofthe contact start switch 20 is manually opened.

The second power control circuit operates the air heating means as wellas the air blower means, the circuit being actuated by closing manualstart switch 25. Closing of start switch 25 energizes time delay relay38 through normally closed contacts 14, 27, and 42. Time delay relay 38includes timing element 39 and normally open contact 43, normally opencontact 43 being operable to a closed position after a predeterminedlength of time, say about three minutes, after energization of timingelement 39.

The remainder of the second power control circuit remains de-energizedduring the time delay except for preheater 61 which is operable inresponse to thermostat means 62. During the three minute time delay, thefuel preheater 61 may be energized during this period by closing thenormally open contact 72, contact 72 being operable to a closed positionupon energizing contact relay 60. Contact relay 60 is in series withcondition responsive thermostat switch 62, condition responsivethermostat switch 62 being in a normally open position, the condition towhich this switch responds being at temperatures below a predeterminedtemperature, such as, for example, 25F. Therefore, if the temperature isbelow 25F., the normally open condition responsive switch 62 will closethereby energizing the contact relay 60 'which closes normally opencontact 72 thereby providing energization of the preheater 61. Thus,preheater 61 has a period of three minutes in which to preheat the fuelfor the heating apparatus.

Upon the closing of contact switch 43 in response to the timing element39, contact relay 37 is energized thereby closing normally open contactswitch 41 and opening normally closed contact switch 42. The opening ofthe normally closed contact switch 42 deenergizes the filament 39 in thetime delay relay 38. Energization of contact relay 37 is maintained,however, in a holding circuit through contact switch 41, contact 37remaining energized even after the time delay relay filament 39 has beende-energized. Energization of contact relay 37, in addition to theopening of switch 42 and closing switch 41, closes normally open switch36 thereby energizing protector relay transformer 76 which suppliesenergy to contact relay 77 through normally closed switches 80 andnormally closed contact switch 56. Energizing of contact relay 77 closesnormally open contact switch 18 thereby energizing the combustion airblower motor 24 and the fuel pump motor 26 through normally closedcontact switches 13 and 23.

A normally open combustion air pressure switch 17 is provided and isoperable to a closed position upon the combustion air blower reaching apredetermined pressure. Upon closing of switch 17, air ventilating fan114 is actuated through the circuit previously described as the firstpower control circuit.

A contact relay 71 is provided for actuating a portion of the circuitincluding a flame detector 81 and a flame detector simulator 82 byoperating normally open switch 74 to a closed position and operatingnormally closed switch to an open position. Contact relay 71 isenergized in response to condition responsive contact switches 65, 66,67, 68 and 69, contact switches 65, 67, and 68 being normally closedswitches and contact switches 66 and 69 being normally open switches.The conditions to which these condition responsive switches respond willbe discussed hereinafter. The contact relay 7] when energized, opensnormally closed switch 75 dropping the flame detector simulator 82 outof circuit and closes normally open switch 74 thereby energizing theflame detector 81.

Flame detector 81 is a flame responsive device having an infinitely highresistance when exposed to a no flame condition and upon exposure to aflame condition the resistance diminishes. Flame detector simulator 82is a simulating device for the flame detector 81 when the flame detector81 is not in operation.

Simulator 82 upon initial energization has an equivalent resistance asflame detector 81 when exposed to flame of, for example, approximately1,000 ohms.

Flame detector 81 and simulator 82 are located in series with a contactrelay 82. Thus, when either detector 81 or simulator 82, depending uponwhich one is being energized and detector 81 senses flame, theresistance in series with contact relay coil 83 is sufficiently lowenough to permit a flow of current to energize relay coil 83 and opencontacts 56, the holding contact 80 remaining in the closed positionkeeping relay coil 77 energized and contacts 18 and 84 remaining closed.Opening of switch 56 deactivates a warp switch heating element 79 andrelay 77 is retained in the energized condition through holding contacts84. Thus, with relay 77 in a closed condition, contacts 18 remain closedkeeping the combustion air blower motor 24, fuel pump motor 26, andventilating fan motor 4 energized.

Furthermore, when flame detector 81 fails to sense the presence of flamewithin the prescribed time, for example seconds, it takes heater 79 toactivate a warp switch which will open switch 80, coils 77 and 83,contacts 18 and 84 thereby de-energizing the combustion air blower motor24. Thus, the opening of switch 80 by the warp switch actuator connectedto heater 79 deactivates the heater and will require manually resettingof switch 80 before the unit can be restarted.

Condition responsive switches which energize contact relay 71 may benormally open or closed switches actuated to their opposite positionupon sensing different conditions during the operation of the equipment.For illustration purposes, switch means 65 is a thermostat switch set toopen in response to the preselected discharge air temperature beingoutside the range of, for example, 140 to 180F.; switches 66 and 68 arepressure switches operable in response to the flow of return air in areturn air duct (not shown), switch 68 being normally closed but openingand switch 66 being normally open but switch 66 closing if the returnair duct is disconnected; and, switch means 67 is a thermostat switchwhich senses the temperature of the return air from a conditional spaceand is set to open in response to the return air from a conditionalspace and is set to open in response to the return air temperature beingoutside the range of, for example, 140 to 180F. Contact switch 69 is anormally open ventilating fan pressure switch which closes when theventilating fan reaches a preselected pressure setting. Therefore, sinceswitch 69 must be closed in order to energize contact relay 71, contactrelay 71 can only be energized after the ventilating fan is up tooperating conditions. Furthermore, the energization of relay 7 1 isdependent upon switch 65 remaining closed in combination with normallyopen switch 66 being actuated to a closed position or switches 67 and 68remaining closed. Thus, if the ventilating fan is up to operationconditions and the return air, if the return air duct is connected, isbetween 140 and 180F., or the discharge air is between 140 and 180F. ifthe return air duct is disconnected, contact relay 71 will be energized.

A time delay relay 30 including timing element 31 is provided, timingfilament 31 being energized through normally closed contact switch 14and any one of the parallel connected normally closed contacts 32, 33,or 34, contact switch 32 being a combustion air pressure switch openingin response to the combustion air blower pressure reaching a preselectedpressure, contact switch 33 being a ventilating fan pressure switchopening in response to the ventilating fan reaching a preselectedpressure, and contact switch 34 opening when the pressure in the fuelpump reaches a preselected setting. All of the preselected pressuresettings for the ventilating fan, the combustion air blower, and thefuel pump are at or below operating conditions whereby under normaloperations the switches 32, 33 and 34 will be open, but if any one ofthe operating conditions are not met the appropriate pressure switchwill remain closed thereby energizing timing element 31.

A time delay relay 46 including timing element 47 and normally opencontact switch means 49 is also provided. Timing element 47 is energizedin response to the closing of either of the normally open conditionresponsive switches 54 and 55 through normally .closed contact switch51, condition responsive switch 54 being, for example, a metal overheatswitch which closes upon the detection of the metal of the heatexchanger becoming dangerously hot and condition responsive switch 55being an air overheat switch which closes upon the detection of adangerously hot air temperature. Since these switches are in parallel,if either one of these conditions are present, the timing filament 47will be energized and after a preselected period of time will closenormally open contact 49 thereby energizing safety relay contactor 16.Safety relay contactor 16 upon energization opens normally closedcontact switch 11, closes normally open contact switch 12, opensnormally closed contact switch 13, opens normally closed contact switch14, and closes normally open contact switch 15. Thus, upon energizationof the safety relay 16, the unit will be de-energized with only the redwarning light 21 being energized through the closing of contact switch12. The unit will remain in this condition until the manual reset switch19 is opened, manual reset switch 19 maintaining energization to contactrelay 16 through closed normally open contact switch 15.

A solenoid valve 50 in parallel with contact relay 71 and actuated inresponse to condition responsive switches 65, 66, 67, 68, and 69, ashereinbefore discussed, is provided to deactuate time delay relay 46 byopening normally closed contact switch means 51. If the ventilating fancombustion air blower and the fuel pump are operating at theirpreselected operating conditions, solenoid valve 50 is energized andnormally closed contact switch means 51 is opened, and normally openswitch means 52 and normally open contact switch means 53 are closed.Once the solenoid valve 50 is energized through normally closed switch53, normally closed'switch 53 is opened and solenoid valve 50 isenergized through contact switch 52. Energization of solenoid valve 50through contact switch 52 removes the solenoid valve 50 from the circuitincluding the aforementioned condition responsive switches. Furthermore,energization of solenoid valve 50 opens normally closed contact switch51 thereby preventing energization of the aforementioned time delayrelay 46. Thus, as long as solenoid valve 50 is energized, time delayrelay 46 is de-energized.

In the operation of the second power control circuit when the startswitch 25 is closed, timing element 39 of time delay 38 is actuatedthrough normally closed contacts 14, 27, and 42. Timing element 39 has adelay of three minutes before it activates nonnally open switch 43 to aclosed position thereby energizing contact relay 37.

During this three minute time delay, if the ambient temperature is below25F. normally open contact switch 62 closes thereby energizing contactrelay 60 through normally closed contacts 147 and 27. Upon energizationof contact relay 60, normally open contact switch 72 closes, therebyenergizing preheater 61 preheater 61 being. for the heating of the fuelfor the fuel pump.

After the three minute time delay of timing element 39, normally openswitch 43 is closed thereby energizing contact relay 37. Uponenergization of contact relay 37, normally open contact switch 41 closesand normally closed contact switch 42 opens, opening of contact switch42 de-energizes timing element 39, but contact switch 41 is in parallelwith switch 42 and maintains the contact relay 37 energized through aholding circuit which includes closed contact switches 41 and 43.Contact relay 37 also closes normally open contact switch 36 therebyestablishing a circuit which includes the combustion air blower motor 24and the pump motor 26. The circuit including the combustion air blowermotor 24 and the fuel pump motor 26 is established through theenergizing of contact relay 77 which closes normally open contact switch18. Contact relay 77 is energized through the secondary side oftransformer 76, normally closed switch 80, safety heater 79, andnormally closed contact switch 56, transformer 76 being actuated by theclosing of contact switch 36.

As soon as the combustion air blower reaches a preselected pressure,normally open switch 17 closes thereby establishing a circuit whichactuates the ventilating air blower. When the ventilating air blowerreaches a preselected operating pressure, normally open contact switch69 will then close thereby energizing contact relay 71. Contact relay 71opens normally closed contact switch 75 dropping the flame detectorsimulator 82 out of the circuit and closes normally open contact switch74 energizing the flame detector 81.

If the combustion air blower, the ventilating fan, or the fuel pumpmotor do not reach their operating conditions, timing element 31 will beenergized and after a preselected period of time will close normallyopen contact switch 29 thereby energizing contact relay 28 whichoperates to open contact switches 27 and 23, and closes contact switch22. Opening switches 27 and 23 de-energizes the combustion air blowerand fuel pump motor. Closing of contact switch 22 energizes warninglight 21. As soon as the contact relay 28 is energized shutting down thecombustion air blower and the fuel pump, relay 28 is de-energizedthereby closing switch 27 which energizes time delay relay 38 throughtiming element 39. At the end of the three minute timing period, timingelement 39 actuates normally open contact switch 43 to a closed positionand the system is reset, recycling itself every three minutes or untilthe condition that prevented the opening of contact switches 32, 33, or34 is corrected.

After the combustion air pressure switch32, the ventilating air pressureswitch 33, and the fuel pump pressure switch 34 have opened, the unit isin the heating mode with the solenoid valve 50 being actuated by thedemand of the thermostats 67 and 65, the thermostat 67 sensing thereturn air from the conditioned space and thermostat 65 maintaining thedischarge air temperature between 140 and 180F. If either of theaforementioned conditions exist and either the normally closed switch 65or 67 opens solenoid valve 50 will not be energized, then timing element47 of time delay relay 46 through normally closed contact 51 may beactuated if switch 54 or 55 closes in response to their preselectedcondition. Timing out of timing element'47 closes normally open contactswitch 49 thereby energizing contact relay 16. Energizing of contactrelay 16 opens contact switches 11, 13 and 14, and closes normally opencontact switch 12 thereby de-energizing the combustion air blower andthe fuel pump and energizing warning light 21. Normally open contactswitch 15 is also closed by the energization of contact delay relay 16thereby maintaining the contact relay 16 in a holding position untilmanual reset switch 19 is opened. Opening of manual reset switch 19de-energizes contact relay 16 thereby actuating normally closed switches11, 13, and 15 to their normally closed positions. Thus, the unit canonly be restarted by manually resetting manually operated switch 19.

Under normal operations, as soon as the ventilating fan reaches thepreselected operating pressure, contact switch 69 closes therebyenergizing contact relay 71 and solenoid valve 50 through normallyclosed contact switch 53, energizing of solenoid valve 50 opens contactswitch 51 and prevents activation of time delay relay 46, relay 46 beingthe actuating device for the contact relay 16. Contact relay 71 uponbeing energized drops out of the circuit the flame detector 82 byopening normally closed contact switch 75 and actuates flame detector 81by closing normally open contact switch 74. As mentioned previously, aslong as the flame detector 81 senses a flame in the burning apparatus,detector 81 will maintain a low enough value of resistance(approximately 1,000 ohms) to allow a minute amount of current to opencontacts 56 with coil 83 cutting off power to the warp switch heater 79.Thus, the unit will continue to operate as long as detector 81 senses aflame in the burning apparatus. However, if the flame goes out, theresistance of the detector 81 increases to an infinitely high value,thus, blocking the current from coil 83 allowing contacts 56 to closeand energize warp switch heater 79, which after a preselected period oftime opens switch deenergizing coil 77 and opening contacts 18 and 84.When contacts 18 open, the combustion air blower motor 24 and the fuelpump 26 are de-energized.

If the ventilating fan does not come up to normal operating conditions,contact switch 69 does not close and flame detector simulator 82 willremain in the circuit, solenoid valve 50 will not close and the unitwill not try to operate as a heater. Furthermore, contacts 33 willremain closed causing time delay 30 to actuate relay coil 28 thru timedelay contacts 29 thereby opening contacts 27 and 23 and closes contacts22. Opening contacts 27 and 23 de-energizes combustion air blower motor24 and fuel pump motor 26. Closing contacts 22 permits the time delay 6to time out and de-energize ventilating air blower motor 4.

What is claimed is:

1. In a control arrangement for an air heater having air blower meansand air heating means and including automatic and manual reset devices;(a) a multi-volt electrical source; (b) a first power control circuitconnected to said source and operable when energized to causeenergization of an air blower means said first power control circuitincluding relay switch means operable in one position to maintainenergization of said first power control circuit under normal operatingconditions and inan opposite position to de-energize said power controlcircuit, said first power control circuit including time delay resetmeans; (c) a second power control circuit connected to said source andoperable when energized to cause energization of said air blower meansand air heating means, said second power control circuit including relayswitch means operable in one position to energize said air heating meansand in an opposite position to de-energize said air heating means; and,((1) said second power control circuit including a time delay means anda thermostat means, said time delay means operable to delay for apreselectedperiod of time energization of said air blower means and airheating means, said thermostat means being operable at a preselected lowtemperature in one position to energize fuel preheat means and in anopposite position to de-energize fuel preheat means during the delay ofsaid time delay means.

2. The control arrangement of claim 1, said second power control circuitincludes time delay means through which a part of said second powercontrol circuit is initially maintained deenergized for a preselectedtime whereby said fuel preheat means is initially energized.

3. The control arrangement of claim 1, said second power control circuitincluding flame detection means whereby upon detection of the loss of aburner flame for said air heating means, said air heating means will bede-energized.

4. The control arrangement of claim 1 including normally closedcondition responsive switch means in parallel, one switch responding toan open position upon said air blower means reaching a preselectedoperating condition, at least one other switch responding to an openposition upon said air heating means reaching preselected operatingcondition, said parallel switches being in series with a time delayrelay means which actuates means to de-energize portions of said secondpower control circuit including said air heating means.

5. The control arrangement of claim 1 including contact relay meansoperable to de-energize said second power control circuit in response tocertain normally open condition responsive switches operating to closedpositions.

6. The control arrangement of claim 1 including a contact relay meansoperable to de-energize a portion of said second power control includingsaid air heating means, said air heating means including a combustionair blower and a fuel pump motor operable in response to the closing ofselected normally open conditions responsive switches.

